1. Field of the Invention
The invention relates to a device for capping jet nozzles of an ink jet printing head by means of a deformable material.
2. Description of the Prior Art
A device of this kind is known from German Auslegeschrift No. 27 02 663. The printing head with its jet nozzles is movable on guide rails along a record carrier for the printing operation. The length of the guide rails exceeds the printing width, so that the printing head is in the rest position at the beginning or at the end of the printing zone during intervals between printing. In order to prevent drying out of the jet nozzles in the rest position, the jet nozzle plates of the printing head are covered by means of a cushion of a substance having viscous elastic properties. Because the printing head is normally linearly moved, the capping device is pivotably mounted on the housing of the ink jet printer outside the printing zone. As soon as the printing head is in the rest position, the capping device is moved in the direction of the jet nozzles, so that the nozzles are capped.
This known capping device offers the advantage that the quick-drying ink penetrates from the jet nozzles into the cavities of the viscous material, thus offering tight sealing of the jet nozzles. Even though the surface deformation of such a substance is normally reversible, a more or less permanent deformation occurs in the case of prolonged use. Therefore, such covering of the jet nozzles is not suitable for long-term use, notably because after the pivoting of the capping device away from the jet nozzles, the ink present on the viscous elastic cushion also dries very quickly and causes a stress on the surface of the cushion which counteracts reversible deformation. This effect can be reduced by pressing the capping device against the jet nozzle with a comparatively high pressure; it is then necessary to increase the pressure as the capping device is used longer. On the other hand, the viscous elastic cushion must be regularly replaced.